Circuit-arrangement comprising a frequency-stabilized oscillator



Dec. 25, 1956 R. BOURGONJON 2,775,703

CIRCUIT-ARRANGEMENT COMPRISING A FREQUENCY-STABILIZED OSCILLATOR FiledMay 18, 1953 :7 J IF H 13/ 1s a L 7: 1:

I 1 MIXER LOW-PASS FILTER '!4 I3 ii NTEGRT'NG NETWORK CRYSTAL-CONTROLLEDPULSE GBJERATOR INVENTOR LOUIS RAYMOND BOLRGONJON AGENTCIRCUIT-ARRANGEMENT COMPRISING A FREQUENCY-STABILIZED OSCILLATOR LouisRaymond Bourgonjon, Hilversum, Netherlands, assignor to HartfordNational Bank and Trust Company, Hartford, Conn., as trustee ApplicationMay 18, 1953, Serial No. 355,778 I Claims priority, applicationNetherlands May 17, 1952 3 Claims. (Cl. 250-36) The present inventionrelates ,to circuit arrangements for stabilizing the frequency of anoscillator. More particularly, the invention relates tocircuit-arrangements comprising an oscillator and equipped withanAFC-circuit-for automatic stabilization of the oscillator frequencyrelatively to a control frequency, more particularly relatively to acomponent of the frequency spectrum of a pulseshaped control voltage,which component is chosen by initial tuning of the oscillator, the saidAFOvoltagecontrolling a reactance tube coupled to the oscillator.

It is known to furnish such arrangements with a search voltage generatorwhich, in the absence of stabilization of the oscillator frequency,produces an oscillator-fre-v quency variation by means of alow-frequency search voltage with a view to extending the collecting'zone of the AFC-circuit.

Circuit-arrangements of this type have been proposed in United StatesPatent No. 2,725,476, issued November 29, 1955, to Hugenholtz, in which,for extending'the collecting zone, the extreme anode direct voltage ofthe reactance tube, which voltage occurs in the absenceof stabilization,serves to energize a saw-tooth generator corn prising a glow dischargetube, the search voltage thus produced causing the reactance tube totraverse the whole control range. In this instance, collection takesplace; only during the slow edge of the sawtooth-search voltage anddilficulties of a practical nature are experiencedin trying to obtain asuificiently constantvery low search frequency. An object of the presentinvention is the provision, in" arrangements of the type referred to inthe preamble, of a simple and particularly suitable search voltagegenerator for widening the collecting zone, which generator produces asinusoidal voltage having a very low fre quency. v1 v t In accordancewith the invention, the search voltage? generator comprises thereactance tube fed back by way of a feedback loop comprising anauxiliary amplifier tube and a circuit-determining the search voltagefrequency. For mutual decoupling of the AFC-circuit andthe searchvoltage circuit on supplying the AFC-voltage to the control grid ofthereactance tube, the coupling ofthe auxiliary amplifying tube to thereactance tube may be established by a cathode resistor which both tubeshave in common and is capacitatively with respect to oscillatorfrequencies. i

As a reactance tube use is preferably made of a multi-grid tube, theoscillator voltage being applied to the control grid, and the feed-backloop being connected between the anode of the reactance tube and anothergrid. The use of two separated grids in the reactance tube forAFC-control and introduction of the search voltage into the reactancetube, respectively, is highly beneficial to the stability of thecircuit-arrangement.

The network determining the search voltage frequency preferably consistsof resistors and capacitors connected in such a manner that thereactance tube and the auxiliary by means of a search voltage generator.In order to.

. 2 amplifying tube jointly constitute a so-called Wien-bridgegenerator.As is known, the frequency constancy of such an RC-generator isparticularly favorable. The RC- gener'ator circuit in accordance Withthe invention is adapted, as will be explained with reference to thedrawing, to be substantially decoupled with respect to the oscillatorfrequencies. This is particularly advantageous for stability reasons.

In order that the invention may be readily carried into effect, it willnow be described with reference to the accompanying drawing, wherein thefigure is a schematic diagram of an embodiment of the circuitarrangement of the present invention.

The circuit-arrangement of the figure comprises a highfrequencyoscillator 1 which is tunable in a range of, for example, 1.5 to 4megacycles per second. The oscillator tube comprises a hexode portion 2of a triodehexode 3. The anode of the hexode is connected through atunable anode circuit 4 to the positive junction terminal 5 of an anodevoltage source (not shown). Coupled to the anode circuit is a feedbackcoil 6 coupled in the .control grid circuit of the hexode.

comprises a feedback capacitor 9 provided between the anode and thecontrol grid of said pentode. To the control grid of the reactance tube7 is applied, by way of a lead 10, an AFC-voltage required forstabilizing the frequency of the high-frequency oscillator 1. The AFCvoltage is applied in such manner that the oscillator frequency isstabilized relatively to a higher harmonic of a pulse voltage from acrystal-controlled pulse generator 11; said harmonic being chosen byinitial tuning of the anode circuit 4. The required AFC-voltage isobtained by mixing, in a mixer stage 12, the voltage set up at theoscillator control grid with the output voltage of the pulse generator11. The mixer stage 12 is normally blocked and is released only duringthe occurrence of a pulse. Said mixer stage acts as a phase-detector andsupplies, via an integrating network 13 and a low-pass filter 14, anAFC-voltage consisting, upon stabilization of the high-frequencyoscillator 1, of a direct voltage and, failing stabilization, of analternating voltage whose frequency corresponds to the frequencydifference of the oscillator voltage and the frequency adjacent spectrumcomponent of the pulse voltage. For various reasons, such as foravoiding instability of the AFC-circuit, the filter elements 13, 14 areso proportioned that only comparatively low difference frequencies, forexample having maxima' of a few kilocycles per second or only afewcollection point is passed. In this instance, the oscillator frequencyis automatically locked on the neighboring higher harmonics of theimpulse spectrum of the pulse generator 11.

The collecting zone of the AFC-circuit is extended establish the searchvoltage generator circuit, a feedback loop is provided between the anodeand the screen grid of the reactance tube 7. Said feedback loopcomprises a triode 15 as an auxiliary amplifying tube and a phasingnetwork, consisting of resistors and capacitors, as the elementdetermining the search voltage frequency. The triode 15 forms part ofthe triode-hexode 3, whose hexode portion serves as an oscillator tube.The anode of the reactance tube 7 is connected through a high-frequencychoke 16 to an input terminal of a four-terminal network grounded at itsinput and output end, whose series impedance consists of theseriesconnection of a resistor 17 and a capacitor 18, and whose parallelimpedance between the output terminals consists of theparallel-connection of a resistor '19 and a capacitor 20. Connectedbetween the'inputterminals.

'part of the reactance tube 7, the"triode"15and the RC-network 17 to 20jointly constitute aso-calledWienbridge-generator with the RC-fourterminal'network 17 to 20 as a frequency-determining element. The lattermay, for example,'be so proportioned as to cause the RC-generator tooscillate with a'frequencyof afew cycles per second.

The RC-generator as described generates" only if the high-frequencyoscillator 1 is not locked on a'spe'ct'rum component, since in lockedcondition, the reactance' tube 7 does not respond to variations of thescreen grid-voltage. That is, said variations cause practically noanodevoltagevariations as required for causing self-oscillation ,of,v theRC-generator. Due to the associated variation of the. apparent reactanceof the reactance tube circuit 8, screen grid voltage variations wouldinvolve variation of the oscillator frequency. Variation oftheoscillator frequency is counteracted by the frequencystabilizingAFC-circuit and thus compensates the influence of the screen gridvoltage variation on the anode current of the reactance tube 7. In otherwords, the reactance tube, in locked condition is negatively fed back toa degree such that the influence of its positive feedback through atriode 15 is offset and the RC-generator is inoperative.

In the absence of locking, however, the RC-generator produces asinusoidal search voltage, with the result that the mutual conductanceof the reactance tube circuit 8, and consequently the frequency of thehigh-frequency oscillator 1, vary in the rhythm of the search voltagefrequency. The high-frequency oscillator 1 then searches, starting withthe tuning frequency of the anode circuit 4, a frequency range of, forexample, approximately50 kilocycles per second, until collection andlocking occurs.

As stated above, the input of the RC-four-terminal network 17 to 201 isdecoupled by means ofthe choke 16' and the short-circuitin'g capacitor21 withrespect to the oscillator frequencies. The output of. saidRC-four terminalnetwork is also short-circuited with respect to theoscillatorfrequencies by the capacitor 20 cnnected between the outputterminals. Owing to this, the usual connection of the control grid ofthe triode 15 to the second control grid of the hexode 2 in thetriode-hexode tube 3 cannot cause trouble. Due to the decouplingcapacitor 23, high frequency voltages will occur neither at the anode ofthe triode 15'nor at the screen grid of the reactance tube 7'. As aresult of the saidf decoupling steps the RC-generator circuit is highly''decoupled relatively to the oscillatorand'reactance-tube circuit andsaid circuits do not adversely affect each other. After locking thefrequency of the highfrequency oscillator 1 on a spectrum component ofthe pulse voltage of the pulse "generator 11, the search voltagegenerator will be fully inoperative. The desired oscillator voltageoccurs across the anode circuit 4 and may be supplied to a load via acoupling capacitor 24.

The invention may also be used if the oscillator frequency is stabilizedrelatively to a sinusoidal control voltage instead of a pulse-shapedcontrol voltage. In this case a sine wave generator instead of the pulsegenerator 11 is connected to the mixer stage -12; the search voltagegenerator circuit may remain unchanged.

It is to be understood that the invention is not limited to the detailsdisclosed but includes all such variations and modifications as fallwithin the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. A system for stabilizing a first voltage produced by a'controll'ableoscillator with respect to a' second voltage produced by a referenceoscillator comprising a phase discriminator for comparing said firstvoltage with'said second voltage and producing therefrom acontrolvoltage dependingon the frequency difference therebetween, avoltage responsivefrequency control device including a Iea'ctance tubehaving an anode, a control grid and a screen grid coupled to' saidcontrollable oscillatorjmeans for applying said control voltage to saidreactance tube to vary the frequency of said' controllable oscillator ina directione'ffe'cting synchronization with said second voltage, and asearch voltage generator'producing a low-frequency search voltage forvarying'the frequency of said controllable oscillator in the absence ofsynchronization, said generator including said reactance tube and afeedback circuit coupled to said tube and comprising a four-terminalnetwork having input terminals and output'terminals, a seriesimpedanceincluding afirst resistor and a first'capacitor seriallyconnected thereto and a parallelimpedance' including as'econd resistorand a second capacitor shunted thereby; a high frequency choke couplingsaid anode to one of said input terminals, a short-circuiting capacitorfor 'saidfirst voltage connected between said'input terminals; and anauxiliary amplifying tube-having an anode and a control grid, saidcontrol grid being connected to one'of said output terminals.

- 2. A system, as 'set forth in claim 1, further including a commonresistor coupling a source of anode" voltage to the anode of saidauxiliary amplifying tubeand to the screen grid of said reactance tube.

' 3. A system, as set forth inc'laim 2, wherein said auxiliaryamplifying tube consists of a t'riod'e'andsaid controllable oscillatorinclude's'an oscillator tubeeonsisting of a hexode and wherein saidtriode and' -said hexode constitute a triode-hexode tube.

References-Cited in'the file ofthis patent UNITED STATES PATENTS

